xref: /openbmc/linux/kernel/exit.c (revision 051d4420)
1  // SPDX-License-Identifier: GPL-2.0-only
2  /*
3   *  linux/kernel/exit.c
4   *
5   *  Copyright (C) 1991, 1992  Linus Torvalds
6   */
7  
8  #include <linux/mm.h>
9  #include <linux/slab.h>
10  #include <linux/sched/autogroup.h>
11  #include <linux/sched/mm.h>
12  #include <linux/sched/stat.h>
13  #include <linux/sched/task.h>
14  #include <linux/sched/task_stack.h>
15  #include <linux/sched/cputime.h>
16  #include <linux/interrupt.h>
17  #include <linux/module.h>
18  #include <linux/capability.h>
19  #include <linux/completion.h>
20  #include <linux/personality.h>
21  #include <linux/tty.h>
22  #include <linux/iocontext.h>
23  #include <linux/key.h>
24  #include <linux/cpu.h>
25  #include <linux/acct.h>
26  #include <linux/tsacct_kern.h>
27  #include <linux/file.h>
28  #include <linux/fdtable.h>
29  #include <linux/freezer.h>
30  #include <linux/binfmts.h>
31  #include <linux/nsproxy.h>
32  #include <linux/pid_namespace.h>
33  #include <linux/ptrace.h>
34  #include <linux/profile.h>
35  #include <linux/mount.h>
36  #include <linux/proc_fs.h>
37  #include <linux/kthread.h>
38  #include <linux/mempolicy.h>
39  #include <linux/taskstats_kern.h>
40  #include <linux/delayacct.h>
41  #include <linux/cgroup.h>
42  #include <linux/syscalls.h>
43  #include <linux/signal.h>
44  #include <linux/posix-timers.h>
45  #include <linux/cn_proc.h>
46  #include <linux/mutex.h>
47  #include <linux/futex.h>
48  #include <linux/pipe_fs_i.h>
49  #include <linux/audit.h> /* for audit_free() */
50  #include <linux/resource.h>
51  #include <linux/task_io_accounting_ops.h>
52  #include <linux/blkdev.h>
53  #include <linux/task_work.h>
54  #include <linux/fs_struct.h>
55  #include <linux/init_task.h>
56  #include <linux/perf_event.h>
57  #include <trace/events/sched.h>
58  #include <linux/hw_breakpoint.h>
59  #include <linux/oom.h>
60  #include <linux/writeback.h>
61  #include <linux/shm.h>
62  #include <linux/kcov.h>
63  #include <linux/kmsan.h>
64  #include <linux/random.h>
65  #include <linux/rcuwait.h>
66  #include <linux/compat.h>
67  #include <linux/io_uring.h>
68  #include <linux/kprobes.h>
69  #include <linux/rethook.h>
70  #include <linux/sysfs.h>
71  
72  #include <linux/uaccess.h>
73  #include <asm/unistd.h>
74  #include <asm/mmu_context.h>
75  
76  /*
77   * The default value should be high enough to not crash a system that randomly
78   * crashes its kernel from time to time, but low enough to at least not permit
79   * overflowing 32-bit refcounts or the ldsem writer count.
80   */
81  static unsigned int oops_limit = 10000;
82  
83  #ifdef CONFIG_SYSCTL
84  static struct ctl_table kern_exit_table[] = {
85  	{
86  		.procname       = "oops_limit",
87  		.data           = &oops_limit,
88  		.maxlen         = sizeof(oops_limit),
89  		.mode           = 0644,
90  		.proc_handler   = proc_douintvec,
91  	},
92  	{ }
93  };
94  
95  static __init int kernel_exit_sysctls_init(void)
96  {
97  	register_sysctl_init("kernel", kern_exit_table);
98  	return 0;
99  }
100  late_initcall(kernel_exit_sysctls_init);
101  #endif
102  
103  static atomic_t oops_count = ATOMIC_INIT(0);
104  
105  #ifdef CONFIG_SYSFS
106  static ssize_t oops_count_show(struct kobject *kobj, struct kobj_attribute *attr,
107  			       char *page)
108  {
109  	return sysfs_emit(page, "%d\n", atomic_read(&oops_count));
110  }
111  
112  static struct kobj_attribute oops_count_attr = __ATTR_RO(oops_count);
113  
114  static __init int kernel_exit_sysfs_init(void)
115  {
116  	sysfs_add_file_to_group(kernel_kobj, &oops_count_attr.attr, NULL);
117  	return 0;
118  }
119  late_initcall(kernel_exit_sysfs_init);
120  #endif
121  
122  static void __unhash_process(struct task_struct *p, bool group_dead)
123  {
124  	nr_threads--;
125  	detach_pid(p, PIDTYPE_PID);
126  	if (group_dead) {
127  		detach_pid(p, PIDTYPE_TGID);
128  		detach_pid(p, PIDTYPE_PGID);
129  		detach_pid(p, PIDTYPE_SID);
130  
131  		list_del_rcu(&p->tasks);
132  		list_del_init(&p->sibling);
133  		__this_cpu_dec(process_counts);
134  	}
135  	list_del_rcu(&p->thread_group);
136  	list_del_rcu(&p->thread_node);
137  }
138  
139  /*
140   * This function expects the tasklist_lock write-locked.
141   */
142  static void __exit_signal(struct task_struct *tsk)
143  {
144  	struct signal_struct *sig = tsk->signal;
145  	bool group_dead = thread_group_leader(tsk);
146  	struct sighand_struct *sighand;
147  	struct tty_struct *tty;
148  	u64 utime, stime;
149  
150  	sighand = rcu_dereference_check(tsk->sighand,
151  					lockdep_tasklist_lock_is_held());
152  	spin_lock(&sighand->siglock);
153  
154  #ifdef CONFIG_POSIX_TIMERS
155  	posix_cpu_timers_exit(tsk);
156  	if (group_dead)
157  		posix_cpu_timers_exit_group(tsk);
158  #endif
159  
160  	if (group_dead) {
161  		tty = sig->tty;
162  		sig->tty = NULL;
163  	} else {
164  		/*
165  		 * If there is any task waiting for the group exit
166  		 * then notify it:
167  		 */
168  		if (sig->notify_count > 0 && !--sig->notify_count)
169  			wake_up_process(sig->group_exec_task);
170  
171  		if (tsk == sig->curr_target)
172  			sig->curr_target = next_thread(tsk);
173  	}
174  
175  	add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
176  			      sizeof(unsigned long long));
177  
178  	/*
179  	 * Accumulate here the counters for all threads as they die. We could
180  	 * skip the group leader because it is the last user of signal_struct,
181  	 * but we want to avoid the race with thread_group_cputime() which can
182  	 * see the empty ->thread_head list.
183  	 */
184  	task_cputime(tsk, &utime, &stime);
185  	write_seqlock(&sig->stats_lock);
186  	sig->utime += utime;
187  	sig->stime += stime;
188  	sig->gtime += task_gtime(tsk);
189  	sig->min_flt += tsk->min_flt;
190  	sig->maj_flt += tsk->maj_flt;
191  	sig->nvcsw += tsk->nvcsw;
192  	sig->nivcsw += tsk->nivcsw;
193  	sig->inblock += task_io_get_inblock(tsk);
194  	sig->oublock += task_io_get_oublock(tsk);
195  	task_io_accounting_add(&sig->ioac, &tsk->ioac);
196  	sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
197  	sig->nr_threads--;
198  	__unhash_process(tsk, group_dead);
199  	write_sequnlock(&sig->stats_lock);
200  
201  	/*
202  	 * Do this under ->siglock, we can race with another thread
203  	 * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
204  	 */
205  	flush_sigqueue(&tsk->pending);
206  	tsk->sighand = NULL;
207  	spin_unlock(&sighand->siglock);
208  
209  	__cleanup_sighand(sighand);
210  	clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
211  	if (group_dead) {
212  		flush_sigqueue(&sig->shared_pending);
213  		tty_kref_put(tty);
214  	}
215  }
216  
217  static void delayed_put_task_struct(struct rcu_head *rhp)
218  {
219  	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
220  
221  	kprobe_flush_task(tsk);
222  	rethook_flush_task(tsk);
223  	perf_event_delayed_put(tsk);
224  	trace_sched_process_free(tsk);
225  	put_task_struct(tsk);
226  }
227  
228  void put_task_struct_rcu_user(struct task_struct *task)
229  {
230  	if (refcount_dec_and_test(&task->rcu_users))
231  		call_rcu(&task->rcu, delayed_put_task_struct);
232  }
233  
234  void __weak release_thread(struct task_struct *dead_task)
235  {
236  }
237  
238  void release_task(struct task_struct *p)
239  {
240  	struct task_struct *leader;
241  	struct pid *thread_pid;
242  	int zap_leader;
243  repeat:
244  	/* don't need to get the RCU readlock here - the process is dead and
245  	 * can't be modifying its own credentials. But shut RCU-lockdep up */
246  	rcu_read_lock();
247  	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
248  	rcu_read_unlock();
249  
250  	cgroup_release(p);
251  
252  	write_lock_irq(&tasklist_lock);
253  	ptrace_release_task(p);
254  	thread_pid = get_pid(p->thread_pid);
255  	__exit_signal(p);
256  
257  	/*
258  	 * If we are the last non-leader member of the thread
259  	 * group, and the leader is zombie, then notify the
260  	 * group leader's parent process. (if it wants notification.)
261  	 */
262  	zap_leader = 0;
263  	leader = p->group_leader;
264  	if (leader != p && thread_group_empty(leader)
265  			&& leader->exit_state == EXIT_ZOMBIE) {
266  		/*
267  		 * If we were the last child thread and the leader has
268  		 * exited already, and the leader's parent ignores SIGCHLD,
269  		 * then we are the one who should release the leader.
270  		 */
271  		zap_leader = do_notify_parent(leader, leader->exit_signal);
272  		if (zap_leader)
273  			leader->exit_state = EXIT_DEAD;
274  	}
275  
276  	write_unlock_irq(&tasklist_lock);
277  	seccomp_filter_release(p);
278  	proc_flush_pid(thread_pid);
279  	put_pid(thread_pid);
280  	release_thread(p);
281  	put_task_struct_rcu_user(p);
282  
283  	p = leader;
284  	if (unlikely(zap_leader))
285  		goto repeat;
286  }
287  
288  int rcuwait_wake_up(struct rcuwait *w)
289  {
290  	int ret = 0;
291  	struct task_struct *task;
292  
293  	rcu_read_lock();
294  
295  	/*
296  	 * Order condition vs @task, such that everything prior to the load
297  	 * of @task is visible. This is the condition as to why the user called
298  	 * rcuwait_wake() in the first place. Pairs with set_current_state()
299  	 * barrier (A) in rcuwait_wait_event().
300  	 *
301  	 *    WAIT                WAKE
302  	 *    [S] tsk = current	  [S] cond = true
303  	 *        MB (A)	      MB (B)
304  	 *    [L] cond		  [L] tsk
305  	 */
306  	smp_mb(); /* (B) */
307  
308  	task = rcu_dereference(w->task);
309  	if (task)
310  		ret = wake_up_process(task);
311  	rcu_read_unlock();
312  
313  	return ret;
314  }
315  EXPORT_SYMBOL_GPL(rcuwait_wake_up);
316  
317  /*
318   * Determine if a process group is "orphaned", according to the POSIX
319   * definition in 2.2.2.52.  Orphaned process groups are not to be affected
320   * by terminal-generated stop signals.  Newly orphaned process groups are
321   * to receive a SIGHUP and a SIGCONT.
322   *
323   * "I ask you, have you ever known what it is to be an orphan?"
324   */
325  static int will_become_orphaned_pgrp(struct pid *pgrp,
326  					struct task_struct *ignored_task)
327  {
328  	struct task_struct *p;
329  
330  	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
331  		if ((p == ignored_task) ||
332  		    (p->exit_state && thread_group_empty(p)) ||
333  		    is_global_init(p->real_parent))
334  			continue;
335  
336  		if (task_pgrp(p->real_parent) != pgrp &&
337  		    task_session(p->real_parent) == task_session(p))
338  			return 0;
339  	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
340  
341  	return 1;
342  }
343  
344  int is_current_pgrp_orphaned(void)
345  {
346  	int retval;
347  
348  	read_lock(&tasklist_lock);
349  	retval = will_become_orphaned_pgrp(task_pgrp(current), NULL);
350  	read_unlock(&tasklist_lock);
351  
352  	return retval;
353  }
354  
355  static bool has_stopped_jobs(struct pid *pgrp)
356  {
357  	struct task_struct *p;
358  
359  	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
360  		if (p->signal->flags & SIGNAL_STOP_STOPPED)
361  			return true;
362  	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
363  
364  	return false;
365  }
366  
367  /*
368   * Check to see if any process groups have become orphaned as
369   * a result of our exiting, and if they have any stopped jobs,
370   * send them a SIGHUP and then a SIGCONT. (POSIX 3.2.2.2)
371   */
372  static void
373  kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent)
374  {
375  	struct pid *pgrp = task_pgrp(tsk);
376  	struct task_struct *ignored_task = tsk;
377  
378  	if (!parent)
379  		/* exit: our father is in a different pgrp than
380  		 * we are and we were the only connection outside.
381  		 */
382  		parent = tsk->real_parent;
383  	else
384  		/* reparent: our child is in a different pgrp than
385  		 * we are, and it was the only connection outside.
386  		 */
387  		ignored_task = NULL;
388  
389  	if (task_pgrp(parent) != pgrp &&
390  	    task_session(parent) == task_session(tsk) &&
391  	    will_become_orphaned_pgrp(pgrp, ignored_task) &&
392  	    has_stopped_jobs(pgrp)) {
393  		__kill_pgrp_info(SIGHUP, SEND_SIG_PRIV, pgrp);
394  		__kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);
395  	}
396  }
397  
398  static void coredump_task_exit(struct task_struct *tsk)
399  {
400  	struct core_state *core_state;
401  
402  	/*
403  	 * Serialize with any possible pending coredump.
404  	 * We must hold siglock around checking core_state
405  	 * and setting PF_POSTCOREDUMP.  The core-inducing thread
406  	 * will increment ->nr_threads for each thread in the
407  	 * group without PF_POSTCOREDUMP set.
408  	 */
409  	spin_lock_irq(&tsk->sighand->siglock);
410  	tsk->flags |= PF_POSTCOREDUMP;
411  	core_state = tsk->signal->core_state;
412  	spin_unlock_irq(&tsk->sighand->siglock);
413  	if (core_state) {
414  		struct core_thread self;
415  
416  		self.task = current;
417  		if (self.task->flags & PF_SIGNALED)
418  			self.next = xchg(&core_state->dumper.next, &self);
419  		else
420  			self.task = NULL;
421  		/*
422  		 * Implies mb(), the result of xchg() must be visible
423  		 * to core_state->dumper.
424  		 */
425  		if (atomic_dec_and_test(&core_state->nr_threads))
426  			complete(&core_state->startup);
427  
428  		for (;;) {
429  			set_current_state(TASK_UNINTERRUPTIBLE|TASK_FREEZABLE);
430  			if (!self.task) /* see coredump_finish() */
431  				break;
432  			schedule();
433  		}
434  		__set_current_state(TASK_RUNNING);
435  	}
436  }
437  
438  #ifdef CONFIG_MEMCG
439  /*
440   * A task is exiting.   If it owned this mm, find a new owner for the mm.
441   */
442  void mm_update_next_owner(struct mm_struct *mm)
443  {
444  	struct task_struct *c, *g, *p = current;
445  
446  retry:
447  	/*
448  	 * If the exiting or execing task is not the owner, it's
449  	 * someone else's problem.
450  	 */
451  	if (mm->owner != p)
452  		return;
453  	/*
454  	 * The current owner is exiting/execing and there are no other
455  	 * candidates.  Do not leave the mm pointing to a possibly
456  	 * freed task structure.
457  	 */
458  	if (atomic_read(&mm->mm_users) <= 1) {
459  		WRITE_ONCE(mm->owner, NULL);
460  		return;
461  	}
462  
463  	read_lock(&tasklist_lock);
464  	/*
465  	 * Search in the children
466  	 */
467  	list_for_each_entry(c, &p->children, sibling) {
468  		if (c->mm == mm)
469  			goto assign_new_owner;
470  	}
471  
472  	/*
473  	 * Search in the siblings
474  	 */
475  	list_for_each_entry(c, &p->real_parent->children, sibling) {
476  		if (c->mm == mm)
477  			goto assign_new_owner;
478  	}
479  
480  	/*
481  	 * Search through everything else, we should not get here often.
482  	 */
483  	for_each_process(g) {
484  		if (g->flags & PF_KTHREAD)
485  			continue;
486  		for_each_thread(g, c) {
487  			if (c->mm == mm)
488  				goto assign_new_owner;
489  			if (c->mm)
490  				break;
491  		}
492  	}
493  	read_unlock(&tasklist_lock);
494  	/*
495  	 * We found no owner yet mm_users > 1: this implies that we are
496  	 * most likely racing with swapoff (try_to_unuse()) or /proc or
497  	 * ptrace or page migration (get_task_mm()).  Mark owner as NULL.
498  	 */
499  	WRITE_ONCE(mm->owner, NULL);
500  	return;
501  
502  assign_new_owner:
503  	BUG_ON(c == p);
504  	get_task_struct(c);
505  	/*
506  	 * The task_lock protects c->mm from changing.
507  	 * We always want mm->owner->mm == mm
508  	 */
509  	task_lock(c);
510  	/*
511  	 * Delay read_unlock() till we have the task_lock()
512  	 * to ensure that c does not slip away underneath us
513  	 */
514  	read_unlock(&tasklist_lock);
515  	if (c->mm != mm) {
516  		task_unlock(c);
517  		put_task_struct(c);
518  		goto retry;
519  	}
520  	WRITE_ONCE(mm->owner, c);
521  	lru_gen_migrate_mm(mm);
522  	task_unlock(c);
523  	put_task_struct(c);
524  }
525  #endif /* CONFIG_MEMCG */
526  
527  /*
528   * Turn us into a lazy TLB process if we
529   * aren't already..
530   */
531  static void exit_mm(void)
532  {
533  	struct mm_struct *mm = current->mm;
534  
535  	exit_mm_release(current, mm);
536  	if (!mm)
537  		return;
538  	sync_mm_rss(mm);
539  	mmap_read_lock(mm);
540  	mmgrab(mm);
541  	BUG_ON(mm != current->active_mm);
542  	/* more a memory barrier than a real lock */
543  	task_lock(current);
544  	/*
545  	 * When a thread stops operating on an address space, the loop
546  	 * in membarrier_private_expedited() may not observe that
547  	 * tsk->mm, and the loop in membarrier_global_expedited() may
548  	 * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED
549  	 * rq->membarrier_state, so those would not issue an IPI.
550  	 * Membarrier requires a memory barrier after accessing
551  	 * user-space memory, before clearing tsk->mm or the
552  	 * rq->membarrier_state.
553  	 */
554  	smp_mb__after_spinlock();
555  	local_irq_disable();
556  	current->mm = NULL;
557  	membarrier_update_current_mm(NULL);
558  	enter_lazy_tlb(mm, current);
559  	local_irq_enable();
560  	task_unlock(current);
561  	mmap_read_unlock(mm);
562  	mm_update_next_owner(mm);
563  	mmput(mm);
564  	if (test_thread_flag(TIF_MEMDIE))
565  		exit_oom_victim();
566  }
567  
568  static struct task_struct *find_alive_thread(struct task_struct *p)
569  {
570  	struct task_struct *t;
571  
572  	for_each_thread(p, t) {
573  		if (!(t->flags & PF_EXITING))
574  			return t;
575  	}
576  	return NULL;
577  }
578  
579  static struct task_struct *find_child_reaper(struct task_struct *father,
580  						struct list_head *dead)
581  	__releases(&tasklist_lock)
582  	__acquires(&tasklist_lock)
583  {
584  	struct pid_namespace *pid_ns = task_active_pid_ns(father);
585  	struct task_struct *reaper = pid_ns->child_reaper;
586  	struct task_struct *p, *n;
587  
588  	if (likely(reaper != father))
589  		return reaper;
590  
591  	reaper = find_alive_thread(father);
592  	if (reaper) {
593  		pid_ns->child_reaper = reaper;
594  		return reaper;
595  	}
596  
597  	write_unlock_irq(&tasklist_lock);
598  
599  	list_for_each_entry_safe(p, n, dead, ptrace_entry) {
600  		list_del_init(&p->ptrace_entry);
601  		release_task(p);
602  	}
603  
604  	zap_pid_ns_processes(pid_ns);
605  	write_lock_irq(&tasklist_lock);
606  
607  	return father;
608  }
609  
610  /*
611   * When we die, we re-parent all our children, and try to:
612   * 1. give them to another thread in our thread group, if such a member exists
613   * 2. give it to the first ancestor process which prctl'd itself as a
614   *    child_subreaper for its children (like a service manager)
615   * 3. give it to the init process (PID 1) in our pid namespace
616   */
617  static struct task_struct *find_new_reaper(struct task_struct *father,
618  					   struct task_struct *child_reaper)
619  {
620  	struct task_struct *thread, *reaper;
621  
622  	thread = find_alive_thread(father);
623  	if (thread)
624  		return thread;
625  
626  	if (father->signal->has_child_subreaper) {
627  		unsigned int ns_level = task_pid(father)->level;
628  		/*
629  		 * Find the first ->is_child_subreaper ancestor in our pid_ns.
630  		 * We can't check reaper != child_reaper to ensure we do not
631  		 * cross the namespaces, the exiting parent could be injected
632  		 * by setns() + fork().
633  		 * We check pid->level, this is slightly more efficient than
634  		 * task_active_pid_ns(reaper) != task_active_pid_ns(father).
635  		 */
636  		for (reaper = father->real_parent;
637  		     task_pid(reaper)->level == ns_level;
638  		     reaper = reaper->real_parent) {
639  			if (reaper == &init_task)
640  				break;
641  			if (!reaper->signal->is_child_subreaper)
642  				continue;
643  			thread = find_alive_thread(reaper);
644  			if (thread)
645  				return thread;
646  		}
647  	}
648  
649  	return child_reaper;
650  }
651  
652  /*
653  * Any that need to be release_task'd are put on the @dead list.
654   */
655  static void reparent_leader(struct task_struct *father, struct task_struct *p,
656  				struct list_head *dead)
657  {
658  	if (unlikely(p->exit_state == EXIT_DEAD))
659  		return;
660  
661  	/* We don't want people slaying init. */
662  	p->exit_signal = SIGCHLD;
663  
664  	/* If it has exited notify the new parent about this child's death. */
665  	if (!p->ptrace &&
666  	    p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
667  		if (do_notify_parent(p, p->exit_signal)) {
668  			p->exit_state = EXIT_DEAD;
669  			list_add(&p->ptrace_entry, dead);
670  		}
671  	}
672  
673  	kill_orphaned_pgrp(p, father);
674  }
675  
676  /*
677   * This does two things:
678   *
679   * A.  Make init inherit all the child processes
680   * B.  Check to see if any process groups have become orphaned
681   *	as a result of our exiting, and if they have any stopped
682   *	jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
683   */
684  static void forget_original_parent(struct task_struct *father,
685  					struct list_head *dead)
686  {
687  	struct task_struct *p, *t, *reaper;
688  
689  	if (unlikely(!list_empty(&father->ptraced)))
690  		exit_ptrace(father, dead);
691  
692  	/* Can drop and reacquire tasklist_lock */
693  	reaper = find_child_reaper(father, dead);
694  	if (list_empty(&father->children))
695  		return;
696  
697  	reaper = find_new_reaper(father, reaper);
698  	list_for_each_entry(p, &father->children, sibling) {
699  		for_each_thread(p, t) {
700  			RCU_INIT_POINTER(t->real_parent, reaper);
701  			BUG_ON((!t->ptrace) != (rcu_access_pointer(t->parent) == father));
702  			if (likely(!t->ptrace))
703  				t->parent = t->real_parent;
704  			if (t->pdeath_signal)
705  				group_send_sig_info(t->pdeath_signal,
706  						    SEND_SIG_NOINFO, t,
707  						    PIDTYPE_TGID);
708  		}
709  		/*
710  		 * If this is a threaded reparent there is no need to
711  		 * notify anyone anything has happened.
712  		 */
713  		if (!same_thread_group(reaper, father))
714  			reparent_leader(father, p, dead);
715  	}
716  	list_splice_tail_init(&father->children, &reaper->children);
717  }
718  
719  /*
720   * Send signals to all our closest relatives so that they know
721   * to properly mourn us..
722   */
723  static void exit_notify(struct task_struct *tsk, int group_dead)
724  {
725  	bool autoreap;
726  	struct task_struct *p, *n;
727  	LIST_HEAD(dead);
728  
729  	write_lock_irq(&tasklist_lock);
730  	forget_original_parent(tsk, &dead);
731  
732  	if (group_dead)
733  		kill_orphaned_pgrp(tsk->group_leader, NULL);
734  
735  	tsk->exit_state = EXIT_ZOMBIE;
736  	if (unlikely(tsk->ptrace)) {
737  		int sig = thread_group_leader(tsk) &&
738  				thread_group_empty(tsk) &&
739  				!ptrace_reparented(tsk) ?
740  			tsk->exit_signal : SIGCHLD;
741  		autoreap = do_notify_parent(tsk, sig);
742  	} else if (thread_group_leader(tsk)) {
743  		autoreap = thread_group_empty(tsk) &&
744  			do_notify_parent(tsk, tsk->exit_signal);
745  	} else {
746  		autoreap = true;
747  	}
748  
749  	if (autoreap) {
750  		tsk->exit_state = EXIT_DEAD;
751  		list_add(&tsk->ptrace_entry, &dead);
752  	}
753  
754  	/* mt-exec, de_thread() is waiting for group leader */
755  	if (unlikely(tsk->signal->notify_count < 0))
756  		wake_up_process(tsk->signal->group_exec_task);
757  	write_unlock_irq(&tasklist_lock);
758  
759  	list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
760  		list_del_init(&p->ptrace_entry);
761  		release_task(p);
762  	}
763  }
764  
765  #ifdef CONFIG_DEBUG_STACK_USAGE
766  static void check_stack_usage(void)
767  {
768  	static DEFINE_SPINLOCK(low_water_lock);
769  	static int lowest_to_date = THREAD_SIZE;
770  	unsigned long free;
771  
772  	free = stack_not_used(current);
773  
774  	if (free >= lowest_to_date)
775  		return;
776  
777  	spin_lock(&low_water_lock);
778  	if (free < lowest_to_date) {
779  		pr_info("%s (%d) used greatest stack depth: %lu bytes left\n",
780  			current->comm, task_pid_nr(current), free);
781  		lowest_to_date = free;
782  	}
783  	spin_unlock(&low_water_lock);
784  }
785  #else
786  static inline void check_stack_usage(void) {}
787  #endif
788  
789  static void synchronize_group_exit(struct task_struct *tsk, long code)
790  {
791  	struct sighand_struct *sighand = tsk->sighand;
792  	struct signal_struct *signal = tsk->signal;
793  
794  	spin_lock_irq(&sighand->siglock);
795  	signal->quick_threads--;
796  	if ((signal->quick_threads == 0) &&
797  	    !(signal->flags & SIGNAL_GROUP_EXIT)) {
798  		signal->flags = SIGNAL_GROUP_EXIT;
799  		signal->group_exit_code = code;
800  		signal->group_stop_count = 0;
801  	}
802  	spin_unlock_irq(&sighand->siglock);
803  }
804  
805  void __noreturn do_exit(long code)
806  {
807  	struct task_struct *tsk = current;
808  	int group_dead;
809  
810  	synchronize_group_exit(tsk, code);
811  
812  	WARN_ON(tsk->plug);
813  
814  	kcov_task_exit(tsk);
815  	kmsan_task_exit(tsk);
816  
817  	coredump_task_exit(tsk);
818  	ptrace_event(PTRACE_EVENT_EXIT, code);
819  
820  	validate_creds_for_do_exit(tsk);
821  
822  	io_uring_files_cancel();
823  	exit_signals(tsk);  /* sets PF_EXITING */
824  
825  	/* sync mm's RSS info before statistics gathering */
826  	if (tsk->mm)
827  		sync_mm_rss(tsk->mm);
828  	acct_update_integrals(tsk);
829  	group_dead = atomic_dec_and_test(&tsk->signal->live);
830  	if (group_dead) {
831  		/*
832  		 * If the last thread of global init has exited, panic
833  		 * immediately to get a useable coredump.
834  		 */
835  		if (unlikely(is_global_init(tsk)))
836  			panic("Attempted to kill init! exitcode=0x%08x\n",
837  				tsk->signal->group_exit_code ?: (int)code);
838  
839  #ifdef CONFIG_POSIX_TIMERS
840  		hrtimer_cancel(&tsk->signal->real_timer);
841  		exit_itimers(tsk);
842  #endif
843  		if (tsk->mm)
844  			setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);
845  	}
846  	acct_collect(code, group_dead);
847  	if (group_dead)
848  		tty_audit_exit();
849  	audit_free(tsk);
850  
851  	tsk->exit_code = code;
852  	taskstats_exit(tsk, group_dead);
853  
854  	exit_mm();
855  
856  	if (group_dead)
857  		acct_process();
858  	trace_sched_process_exit(tsk);
859  
860  	exit_sem(tsk);
861  	exit_shm(tsk);
862  	exit_files(tsk);
863  	exit_fs(tsk);
864  	if (group_dead)
865  		disassociate_ctty(1);
866  	exit_task_namespaces(tsk);
867  	exit_task_work(tsk);
868  	exit_thread(tsk);
869  
870  	/*
871  	 * Flush inherited counters to the parent - before the parent
872  	 * gets woken up by child-exit notifications.
873  	 *
874  	 * because of cgroup mode, must be called before cgroup_exit()
875  	 */
876  	perf_event_exit_task(tsk);
877  
878  	sched_autogroup_exit_task(tsk);
879  	cgroup_exit(tsk);
880  
881  	/*
882  	 * FIXME: do that only when needed, using sched_exit tracepoint
883  	 */
884  	flush_ptrace_hw_breakpoint(tsk);
885  
886  	exit_tasks_rcu_start();
887  	exit_notify(tsk, group_dead);
888  	proc_exit_connector(tsk);
889  	mpol_put_task_policy(tsk);
890  #ifdef CONFIG_FUTEX
891  	if (unlikely(current->pi_state_cache))
892  		kfree(current->pi_state_cache);
893  #endif
894  	/*
895  	 * Make sure we are holding no locks:
896  	 */
897  	debug_check_no_locks_held();
898  
899  	if (tsk->io_context)
900  		exit_io_context(tsk);
901  
902  	if (tsk->splice_pipe)
903  		free_pipe_info(tsk->splice_pipe);
904  
905  	if (tsk->task_frag.page)
906  		put_page(tsk->task_frag.page);
907  
908  	validate_creds_for_do_exit(tsk);
909  	exit_task_stack_account(tsk);
910  
911  	check_stack_usage();
912  	preempt_disable();
913  	if (tsk->nr_dirtied)
914  		__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
915  	exit_rcu();
916  	exit_tasks_rcu_finish();
917  
918  	lockdep_free_task(tsk);
919  	do_task_dead();
920  }
921  
922  void __noreturn make_task_dead(int signr)
923  {
924  	/*
925  	 * Take the task off the cpu after something catastrophic has
926  	 * happened.
927  	 *
928  	 * We can get here from a kernel oops, sometimes with preemption off.
929  	 * Start by checking for critical errors.
930  	 * Then fix up important state like USER_DS and preemption.
931  	 * Then do everything else.
932  	 */
933  	struct task_struct *tsk = current;
934  	unsigned int limit;
935  
936  	if (unlikely(in_interrupt()))
937  		panic("Aiee, killing interrupt handler!");
938  	if (unlikely(!tsk->pid))
939  		panic("Attempted to kill the idle task!");
940  
941  	if (unlikely(in_atomic())) {
942  		pr_info("note: %s[%d] exited with preempt_count %d\n",
943  			current->comm, task_pid_nr(current),
944  			preempt_count());
945  		preempt_count_set(PREEMPT_ENABLED);
946  	}
947  
948  	/*
949  	 * Every time the system oopses, if the oops happens while a reference
950  	 * to an object was held, the reference leaks.
951  	 * If the oops doesn't also leak memory, repeated oopsing can cause
952  	 * reference counters to wrap around (if they're not using refcount_t).
953  	 * This means that repeated oopsing can make unexploitable-looking bugs
954  	 * exploitable through repeated oopsing.
955  	 * To make sure this can't happen, place an upper bound on how often the
956  	 * kernel may oops without panic().
957  	 */
958  	limit = READ_ONCE(oops_limit);
959  	if (atomic_inc_return(&oops_count) >= limit && limit)
960  		panic("Oopsed too often (kernel.oops_limit is %d)", limit);
961  
962  	/*
963  	 * We're taking recursive faults here in make_task_dead. Safest is to just
964  	 * leave this task alone and wait for reboot.
965  	 */
966  	if (unlikely(tsk->flags & PF_EXITING)) {
967  		pr_alert("Fixing recursive fault but reboot is needed!\n");
968  		futex_exit_recursive(tsk);
969  		tsk->exit_state = EXIT_DEAD;
970  		refcount_inc(&tsk->rcu_users);
971  		do_task_dead();
972  	}
973  
974  	do_exit(signr);
975  }
976  
977  SYSCALL_DEFINE1(exit, int, error_code)
978  {
979  	do_exit((error_code&0xff)<<8);
980  }
981  
982  /*
983   * Take down every thread in the group.  This is called by fatal signals
984   * as well as by sys_exit_group (below).
985   */
986  void __noreturn
987  do_group_exit(int exit_code)
988  {
989  	struct signal_struct *sig = current->signal;
990  
991  	if (sig->flags & SIGNAL_GROUP_EXIT)
992  		exit_code = sig->group_exit_code;
993  	else if (sig->group_exec_task)
994  		exit_code = 0;
995  	else {
996  		struct sighand_struct *const sighand = current->sighand;
997  
998  		spin_lock_irq(&sighand->siglock);
999  		if (sig->flags & SIGNAL_GROUP_EXIT)
1000  			/* Another thread got here before we took the lock.  */
1001  			exit_code = sig->group_exit_code;
1002  		else if (sig->group_exec_task)
1003  			exit_code = 0;
1004  		else {
1005  			sig->group_exit_code = exit_code;
1006  			sig->flags = SIGNAL_GROUP_EXIT;
1007  			zap_other_threads(current);
1008  		}
1009  		spin_unlock_irq(&sighand->siglock);
1010  	}
1011  
1012  	do_exit(exit_code);
1013  	/* NOTREACHED */
1014  }
1015  
1016  /*
1017   * this kills every thread in the thread group. Note that any externally
1018   * wait4()-ing process will get the correct exit code - even if this
1019   * thread is not the thread group leader.
1020   */
1021  SYSCALL_DEFINE1(exit_group, int, error_code)
1022  {
1023  	do_group_exit((error_code & 0xff) << 8);
1024  	/* NOTREACHED */
1025  	return 0;
1026  }
1027  
1028  struct waitid_info {
1029  	pid_t pid;
1030  	uid_t uid;
1031  	int status;
1032  	int cause;
1033  };
1034  
1035  struct wait_opts {
1036  	enum pid_type		wo_type;
1037  	int			wo_flags;
1038  	struct pid		*wo_pid;
1039  
1040  	struct waitid_info	*wo_info;
1041  	int			wo_stat;
1042  	struct rusage		*wo_rusage;
1043  
1044  	wait_queue_entry_t		child_wait;
1045  	int			notask_error;
1046  };
1047  
1048  static int eligible_pid(struct wait_opts *wo, struct task_struct *p)
1049  {
1050  	return	wo->wo_type == PIDTYPE_MAX ||
1051  		task_pid_type(p, wo->wo_type) == wo->wo_pid;
1052  }
1053  
1054  static int
1055  eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p)
1056  {
1057  	if (!eligible_pid(wo, p))
1058  		return 0;
1059  
1060  	/*
1061  	 * Wait for all children (clone and not) if __WALL is set or
1062  	 * if it is traced by us.
1063  	 */
1064  	if (ptrace || (wo->wo_flags & __WALL))
1065  		return 1;
1066  
1067  	/*
1068  	 * Otherwise, wait for clone children *only* if __WCLONE is set;
1069  	 * otherwise, wait for non-clone children *only*.
1070  	 *
1071  	 * Note: a "clone" child here is one that reports to its parent
1072  	 * using a signal other than SIGCHLD, or a non-leader thread which
1073  	 * we can only see if it is traced by us.
1074  	 */
1075  	if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
1076  		return 0;
1077  
1078  	return 1;
1079  }
1080  
1081  /*
1082   * Handle sys_wait4 work for one task in state EXIT_ZOMBIE.  We hold
1083   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
1084   * the lock and this task is uninteresting.  If we return nonzero, we have
1085   * released the lock and the system call should return.
1086   */
1087  static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
1088  {
1089  	int state, status;
1090  	pid_t pid = task_pid_vnr(p);
1091  	uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p));
1092  	struct waitid_info *infop;
1093  
1094  	if (!likely(wo->wo_flags & WEXITED))
1095  		return 0;
1096  
1097  	if (unlikely(wo->wo_flags & WNOWAIT)) {
1098  		status = (p->signal->flags & SIGNAL_GROUP_EXIT)
1099  			? p->signal->group_exit_code : p->exit_code;
1100  		get_task_struct(p);
1101  		read_unlock(&tasklist_lock);
1102  		sched_annotate_sleep();
1103  		if (wo->wo_rusage)
1104  			getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1105  		put_task_struct(p);
1106  		goto out_info;
1107  	}
1108  	/*
1109  	 * Move the task's state to DEAD/TRACE, only one thread can do this.
1110  	 */
1111  	state = (ptrace_reparented(p) && thread_group_leader(p)) ?
1112  		EXIT_TRACE : EXIT_DEAD;
1113  	if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
1114  		return 0;
1115  	/*
1116  	 * We own this thread, nobody else can reap it.
1117  	 */
1118  	read_unlock(&tasklist_lock);
1119  	sched_annotate_sleep();
1120  
1121  	/*
1122  	 * Check thread_group_leader() to exclude the traced sub-threads.
1123  	 */
1124  	if (state == EXIT_DEAD && thread_group_leader(p)) {
1125  		struct signal_struct *sig = p->signal;
1126  		struct signal_struct *psig = current->signal;
1127  		unsigned long maxrss;
1128  		u64 tgutime, tgstime;
1129  
1130  		/*
1131  		 * The resource counters for the group leader are in its
1132  		 * own task_struct.  Those for dead threads in the group
1133  		 * are in its signal_struct, as are those for the child
1134  		 * processes it has previously reaped.  All these
1135  		 * accumulate in the parent's signal_struct c* fields.
1136  		 *
1137  		 * We don't bother to take a lock here to protect these
1138  		 * p->signal fields because the whole thread group is dead
1139  		 * and nobody can change them.
1140  		 *
1141  		 * psig->stats_lock also protects us from our sub-threads
1142  		 * which can reap other children at the same time. Until
1143  		 * we change k_getrusage()-like users to rely on this lock
1144  		 * we have to take ->siglock as well.
1145  		 *
1146  		 * We use thread_group_cputime_adjusted() to get times for
1147  		 * the thread group, which consolidates times for all threads
1148  		 * in the group including the group leader.
1149  		 */
1150  		thread_group_cputime_adjusted(p, &tgutime, &tgstime);
1151  		spin_lock_irq(&current->sighand->siglock);
1152  		write_seqlock(&psig->stats_lock);
1153  		psig->cutime += tgutime + sig->cutime;
1154  		psig->cstime += tgstime + sig->cstime;
1155  		psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
1156  		psig->cmin_flt +=
1157  			p->min_flt + sig->min_flt + sig->cmin_flt;
1158  		psig->cmaj_flt +=
1159  			p->maj_flt + sig->maj_flt + sig->cmaj_flt;
1160  		psig->cnvcsw +=
1161  			p->nvcsw + sig->nvcsw + sig->cnvcsw;
1162  		psig->cnivcsw +=
1163  			p->nivcsw + sig->nivcsw + sig->cnivcsw;
1164  		psig->cinblock +=
1165  			task_io_get_inblock(p) +
1166  			sig->inblock + sig->cinblock;
1167  		psig->coublock +=
1168  			task_io_get_oublock(p) +
1169  			sig->oublock + sig->coublock;
1170  		maxrss = max(sig->maxrss, sig->cmaxrss);
1171  		if (psig->cmaxrss < maxrss)
1172  			psig->cmaxrss = maxrss;
1173  		task_io_accounting_add(&psig->ioac, &p->ioac);
1174  		task_io_accounting_add(&psig->ioac, &sig->ioac);
1175  		write_sequnlock(&psig->stats_lock);
1176  		spin_unlock_irq(&current->sighand->siglock);
1177  	}
1178  
1179  	if (wo->wo_rusage)
1180  		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1181  	status = (p->signal->flags & SIGNAL_GROUP_EXIT)
1182  		? p->signal->group_exit_code : p->exit_code;
1183  	wo->wo_stat = status;
1184  
1185  	if (state == EXIT_TRACE) {
1186  		write_lock_irq(&tasklist_lock);
1187  		/* We dropped tasklist, ptracer could die and untrace */
1188  		ptrace_unlink(p);
1189  
1190  		/* If parent wants a zombie, don't release it now */
1191  		state = EXIT_ZOMBIE;
1192  		if (do_notify_parent(p, p->exit_signal))
1193  			state = EXIT_DEAD;
1194  		p->exit_state = state;
1195  		write_unlock_irq(&tasklist_lock);
1196  	}
1197  	if (state == EXIT_DEAD)
1198  		release_task(p);
1199  
1200  out_info:
1201  	infop = wo->wo_info;
1202  	if (infop) {
1203  		if ((status & 0x7f) == 0) {
1204  			infop->cause = CLD_EXITED;
1205  			infop->status = status >> 8;
1206  		} else {
1207  			infop->cause = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
1208  			infop->status = status & 0x7f;
1209  		}
1210  		infop->pid = pid;
1211  		infop->uid = uid;
1212  	}
1213  
1214  	return pid;
1215  }
1216  
1217  static int *task_stopped_code(struct task_struct *p, bool ptrace)
1218  {
1219  	if (ptrace) {
1220  		if (task_is_traced(p) && !(p->jobctl & JOBCTL_LISTENING))
1221  			return &p->exit_code;
1222  	} else {
1223  		if (p->signal->flags & SIGNAL_STOP_STOPPED)
1224  			return &p->signal->group_exit_code;
1225  	}
1226  	return NULL;
1227  }
1228  
1229  /**
1230   * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
1231   * @wo: wait options
1232   * @ptrace: is the wait for ptrace
1233   * @p: task to wait for
1234   *
1235   * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
1236   *
1237   * CONTEXT:
1238   * read_lock(&tasklist_lock), which is released if return value is
1239   * non-zero.  Also, grabs and releases @p->sighand->siglock.
1240   *
1241   * RETURNS:
1242   * 0 if wait condition didn't exist and search for other wait conditions
1243   * should continue.  Non-zero return, -errno on failure and @p's pid on
1244   * success, implies that tasklist_lock is released and wait condition
1245   * search should terminate.
1246   */
1247  static int wait_task_stopped(struct wait_opts *wo,
1248  				int ptrace, struct task_struct *p)
1249  {
1250  	struct waitid_info *infop;
1251  	int exit_code, *p_code, why;
1252  	uid_t uid = 0; /* unneeded, required by compiler */
1253  	pid_t pid;
1254  
1255  	/*
1256  	 * Traditionally we see ptrace'd stopped tasks regardless of options.
1257  	 */
1258  	if (!ptrace && !(wo->wo_flags & WUNTRACED))
1259  		return 0;
1260  
1261  	if (!task_stopped_code(p, ptrace))
1262  		return 0;
1263  
1264  	exit_code = 0;
1265  	spin_lock_irq(&p->sighand->siglock);
1266  
1267  	p_code = task_stopped_code(p, ptrace);
1268  	if (unlikely(!p_code))
1269  		goto unlock_sig;
1270  
1271  	exit_code = *p_code;
1272  	if (!exit_code)
1273  		goto unlock_sig;
1274  
1275  	if (!unlikely(wo->wo_flags & WNOWAIT))
1276  		*p_code = 0;
1277  
1278  	uid = from_kuid_munged(current_user_ns(), task_uid(p));
1279  unlock_sig:
1280  	spin_unlock_irq(&p->sighand->siglock);
1281  	if (!exit_code)
1282  		return 0;
1283  
1284  	/*
1285  	 * Now we are pretty sure this task is interesting.
1286  	 * Make sure it doesn't get reaped out from under us while we
1287  	 * give up the lock and then examine it below.  We don't want to
1288  	 * keep holding onto the tasklist_lock while we call getrusage and
1289  	 * possibly take page faults for user memory.
1290  	 */
1291  	get_task_struct(p);
1292  	pid = task_pid_vnr(p);
1293  	why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
1294  	read_unlock(&tasklist_lock);
1295  	sched_annotate_sleep();
1296  	if (wo->wo_rusage)
1297  		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1298  	put_task_struct(p);
1299  
1300  	if (likely(!(wo->wo_flags & WNOWAIT)))
1301  		wo->wo_stat = (exit_code << 8) | 0x7f;
1302  
1303  	infop = wo->wo_info;
1304  	if (infop) {
1305  		infop->cause = why;
1306  		infop->status = exit_code;
1307  		infop->pid = pid;
1308  		infop->uid = uid;
1309  	}
1310  	return pid;
1311  }
1312  
1313  /*
1314   * Handle do_wait work for one task in a live, non-stopped state.
1315   * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
1316   * the lock and this task is uninteresting.  If we return nonzero, we have
1317   * released the lock and the system call should return.
1318   */
1319  static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
1320  {
1321  	struct waitid_info *infop;
1322  	pid_t pid;
1323  	uid_t uid;
1324  
1325  	if (!unlikely(wo->wo_flags & WCONTINUED))
1326  		return 0;
1327  
1328  	if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
1329  		return 0;
1330  
1331  	spin_lock_irq(&p->sighand->siglock);
1332  	/* Re-check with the lock held.  */
1333  	if (!(p->signal->flags & SIGNAL_STOP_CONTINUED)) {
1334  		spin_unlock_irq(&p->sighand->siglock);
1335  		return 0;
1336  	}
1337  	if (!unlikely(wo->wo_flags & WNOWAIT))
1338  		p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
1339  	uid = from_kuid_munged(current_user_ns(), task_uid(p));
1340  	spin_unlock_irq(&p->sighand->siglock);
1341  
1342  	pid = task_pid_vnr(p);
1343  	get_task_struct(p);
1344  	read_unlock(&tasklist_lock);
1345  	sched_annotate_sleep();
1346  	if (wo->wo_rusage)
1347  		getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1348  	put_task_struct(p);
1349  
1350  	infop = wo->wo_info;
1351  	if (!infop) {
1352  		wo->wo_stat = 0xffff;
1353  	} else {
1354  		infop->cause = CLD_CONTINUED;
1355  		infop->pid = pid;
1356  		infop->uid = uid;
1357  		infop->status = SIGCONT;
1358  	}
1359  	return pid;
1360  }
1361  
1362  /*
1363   * Consider @p for a wait by @parent.
1364   *
1365   * -ECHILD should be in ->notask_error before the first call.
1366   * Returns nonzero for a final return, when we have unlocked tasklist_lock.
1367   * Returns zero if the search for a child should continue;
1368   * then ->notask_error is 0 if @p is an eligible child,
1369   * or still -ECHILD.
1370   */
1371  static int wait_consider_task(struct wait_opts *wo, int ptrace,
1372  				struct task_struct *p)
1373  {
1374  	/*
1375  	 * We can race with wait_task_zombie() from another thread.
1376  	 * Ensure that EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE transition
1377  	 * can't confuse the checks below.
1378  	 */
1379  	int exit_state = READ_ONCE(p->exit_state);
1380  	int ret;
1381  
1382  	if (unlikely(exit_state == EXIT_DEAD))
1383  		return 0;
1384  
1385  	ret = eligible_child(wo, ptrace, p);
1386  	if (!ret)
1387  		return ret;
1388  
1389  	if (unlikely(exit_state == EXIT_TRACE)) {
1390  		/*
1391  		 * ptrace == 0 means we are the natural parent. In this case
1392  		 * we should clear notask_error, debugger will notify us.
1393  		 */
1394  		if (likely(!ptrace))
1395  			wo->notask_error = 0;
1396  		return 0;
1397  	}
1398  
1399  	if (likely(!ptrace) && unlikely(p->ptrace)) {
1400  		/*
1401  		 * If it is traced by its real parent's group, just pretend
1402  		 * the caller is ptrace_do_wait() and reap this child if it
1403  		 * is zombie.
1404  		 *
1405  		 * This also hides group stop state from real parent; otherwise
1406  		 * a single stop can be reported twice as group and ptrace stop.
1407  		 * If a ptracer wants to distinguish these two events for its
1408  		 * own children it should create a separate process which takes
1409  		 * the role of real parent.
1410  		 */
1411  		if (!ptrace_reparented(p))
1412  			ptrace = 1;
1413  	}
1414  
1415  	/* slay zombie? */
1416  	if (exit_state == EXIT_ZOMBIE) {
1417  		/* we don't reap group leaders with subthreads */
1418  		if (!delay_group_leader(p)) {
1419  			/*
1420  			 * A zombie ptracee is only visible to its ptracer.
1421  			 * Notification and reaping will be cascaded to the
1422  			 * real parent when the ptracer detaches.
1423  			 */
1424  			if (unlikely(ptrace) || likely(!p->ptrace))
1425  				return wait_task_zombie(wo, p);
1426  		}
1427  
1428  		/*
1429  		 * Allow access to stopped/continued state via zombie by
1430  		 * falling through.  Clearing of notask_error is complex.
1431  		 *
1432  		 * When !@ptrace:
1433  		 *
1434  		 * If WEXITED is set, notask_error should naturally be
1435  		 * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
1436  		 * so, if there are live subthreads, there are events to
1437  		 * wait for.  If all subthreads are dead, it's still safe
1438  		 * to clear - this function will be called again in finite
1439  		 * amount time once all the subthreads are released and
1440  		 * will then return without clearing.
1441  		 *
1442  		 * When @ptrace:
1443  		 *
1444  		 * Stopped state is per-task and thus can't change once the
1445  		 * target task dies.  Only continued and exited can happen.
1446  		 * Clear notask_error if WCONTINUED | WEXITED.
1447  		 */
1448  		if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
1449  			wo->notask_error = 0;
1450  	} else {
1451  		/*
1452  		 * @p is alive and it's gonna stop, continue or exit, so
1453  		 * there always is something to wait for.
1454  		 */
1455  		wo->notask_error = 0;
1456  	}
1457  
1458  	/*
1459  	 * Wait for stopped.  Depending on @ptrace, different stopped state
1460  	 * is used and the two don't interact with each other.
1461  	 */
1462  	ret = wait_task_stopped(wo, ptrace, p);
1463  	if (ret)
1464  		return ret;
1465  
1466  	/*
1467  	 * Wait for continued.  There's only one continued state and the
1468  	 * ptracer can consume it which can confuse the real parent.  Don't
1469  	 * use WCONTINUED from ptracer.  You don't need or want it.
1470  	 */
1471  	return wait_task_continued(wo, p);
1472  }
1473  
1474  /*
1475   * Do the work of do_wait() for one thread in the group, @tsk.
1476   *
1477   * -ECHILD should be in ->notask_error before the first call.
1478   * Returns nonzero for a final return, when we have unlocked tasklist_lock.
1479   * Returns zero if the search for a child should continue; then
1480   * ->notask_error is 0 if there were any eligible children,
1481   * or still -ECHILD.
1482   */
1483  static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
1484  {
1485  	struct task_struct *p;
1486  
1487  	list_for_each_entry(p, &tsk->children, sibling) {
1488  		int ret = wait_consider_task(wo, 0, p);
1489  
1490  		if (ret)
1491  			return ret;
1492  	}
1493  
1494  	return 0;
1495  }
1496  
1497  static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk)
1498  {
1499  	struct task_struct *p;
1500  
1501  	list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
1502  		int ret = wait_consider_task(wo, 1, p);
1503  
1504  		if (ret)
1505  			return ret;
1506  	}
1507  
1508  	return 0;
1509  }
1510  
1511  static int child_wait_callback(wait_queue_entry_t *wait, unsigned mode,
1512  				int sync, void *key)
1513  {
1514  	struct wait_opts *wo = container_of(wait, struct wait_opts,
1515  						child_wait);
1516  	struct task_struct *p = key;
1517  
1518  	if (!eligible_pid(wo, p))
1519  		return 0;
1520  
1521  	if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
1522  		return 0;
1523  
1524  	return default_wake_function(wait, mode, sync, key);
1525  }
1526  
1527  void __wake_up_parent(struct task_struct *p, struct task_struct *parent)
1528  {
1529  	__wake_up_sync_key(&parent->signal->wait_chldexit,
1530  			   TASK_INTERRUPTIBLE, p);
1531  }
1532  
1533  static bool is_effectively_child(struct wait_opts *wo, bool ptrace,
1534  				 struct task_struct *target)
1535  {
1536  	struct task_struct *parent =
1537  		!ptrace ? target->real_parent : target->parent;
1538  
1539  	return current == parent || (!(wo->wo_flags & __WNOTHREAD) &&
1540  				     same_thread_group(current, parent));
1541  }
1542  
1543  /*
1544   * Optimization for waiting on PIDTYPE_PID. No need to iterate through child
1545   * and tracee lists to find the target task.
1546   */
1547  static int do_wait_pid(struct wait_opts *wo)
1548  {
1549  	bool ptrace;
1550  	struct task_struct *target;
1551  	int retval;
1552  
1553  	ptrace = false;
1554  	target = pid_task(wo->wo_pid, PIDTYPE_TGID);
1555  	if (target && is_effectively_child(wo, ptrace, target)) {
1556  		retval = wait_consider_task(wo, ptrace, target);
1557  		if (retval)
1558  			return retval;
1559  	}
1560  
1561  	ptrace = true;
1562  	target = pid_task(wo->wo_pid, PIDTYPE_PID);
1563  	if (target && target->ptrace &&
1564  	    is_effectively_child(wo, ptrace, target)) {
1565  		retval = wait_consider_task(wo, ptrace, target);
1566  		if (retval)
1567  			return retval;
1568  	}
1569  
1570  	return 0;
1571  }
1572  
1573  static long do_wait(struct wait_opts *wo)
1574  {
1575  	int retval;
1576  
1577  	trace_sched_process_wait(wo->wo_pid);
1578  
1579  	init_waitqueue_func_entry(&wo->child_wait, child_wait_callback);
1580  	wo->child_wait.private = current;
1581  	add_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
1582  repeat:
1583  	/*
1584  	 * If there is nothing that can match our criteria, just get out.
1585  	 * We will clear ->notask_error to zero if we see any child that
1586  	 * might later match our criteria, even if we are not able to reap
1587  	 * it yet.
1588  	 */
1589  	wo->notask_error = -ECHILD;
1590  	if ((wo->wo_type < PIDTYPE_MAX) &&
1591  	   (!wo->wo_pid || !pid_has_task(wo->wo_pid, wo->wo_type)))
1592  		goto notask;
1593  
1594  	set_current_state(TASK_INTERRUPTIBLE);
1595  	read_lock(&tasklist_lock);
1596  
1597  	if (wo->wo_type == PIDTYPE_PID) {
1598  		retval = do_wait_pid(wo);
1599  		if (retval)
1600  			goto end;
1601  	} else {
1602  		struct task_struct *tsk = current;
1603  
1604  		do {
1605  			retval = do_wait_thread(wo, tsk);
1606  			if (retval)
1607  				goto end;
1608  
1609  			retval = ptrace_do_wait(wo, tsk);
1610  			if (retval)
1611  				goto end;
1612  
1613  			if (wo->wo_flags & __WNOTHREAD)
1614  				break;
1615  		} while_each_thread(current, tsk);
1616  	}
1617  	read_unlock(&tasklist_lock);
1618  
1619  notask:
1620  	retval = wo->notask_error;
1621  	if (!retval && !(wo->wo_flags & WNOHANG)) {
1622  		retval = -ERESTARTSYS;
1623  		if (!signal_pending(current)) {
1624  			schedule();
1625  			goto repeat;
1626  		}
1627  	}
1628  end:
1629  	__set_current_state(TASK_RUNNING);
1630  	remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
1631  	return retval;
1632  }
1633  
1634  static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
1635  			  int options, struct rusage *ru)
1636  {
1637  	struct wait_opts wo;
1638  	struct pid *pid = NULL;
1639  	enum pid_type type;
1640  	long ret;
1641  	unsigned int f_flags = 0;
1642  
1643  	if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED|
1644  			__WNOTHREAD|__WCLONE|__WALL))
1645  		return -EINVAL;
1646  	if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
1647  		return -EINVAL;
1648  
1649  	switch (which) {
1650  	case P_ALL:
1651  		type = PIDTYPE_MAX;
1652  		break;
1653  	case P_PID:
1654  		type = PIDTYPE_PID;
1655  		if (upid <= 0)
1656  			return -EINVAL;
1657  
1658  		pid = find_get_pid(upid);
1659  		break;
1660  	case P_PGID:
1661  		type = PIDTYPE_PGID;
1662  		if (upid < 0)
1663  			return -EINVAL;
1664  
1665  		if (upid)
1666  			pid = find_get_pid(upid);
1667  		else
1668  			pid = get_task_pid(current, PIDTYPE_PGID);
1669  		break;
1670  	case P_PIDFD:
1671  		type = PIDTYPE_PID;
1672  		if (upid < 0)
1673  			return -EINVAL;
1674  
1675  		pid = pidfd_get_pid(upid, &f_flags);
1676  		if (IS_ERR(pid))
1677  			return PTR_ERR(pid);
1678  
1679  		break;
1680  	default:
1681  		return -EINVAL;
1682  	}
1683  
1684  	wo.wo_type	= type;
1685  	wo.wo_pid	= pid;
1686  	wo.wo_flags	= options;
1687  	wo.wo_info	= infop;
1688  	wo.wo_rusage	= ru;
1689  	if (f_flags & O_NONBLOCK)
1690  		wo.wo_flags |= WNOHANG;
1691  
1692  	ret = do_wait(&wo);
1693  	if (!ret && !(options & WNOHANG) && (f_flags & O_NONBLOCK))
1694  		ret = -EAGAIN;
1695  
1696  	put_pid(pid);
1697  	return ret;
1698  }
1699  
1700  SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
1701  		infop, int, options, struct rusage __user *, ru)
1702  {
1703  	struct rusage r;
1704  	struct waitid_info info = {.status = 0};
1705  	long err = kernel_waitid(which, upid, &info, options, ru ? &r : NULL);
1706  	int signo = 0;
1707  
1708  	if (err > 0) {
1709  		signo = SIGCHLD;
1710  		err = 0;
1711  		if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
1712  			return -EFAULT;
1713  	}
1714  	if (!infop)
1715  		return err;
1716  
1717  	if (!user_write_access_begin(infop, sizeof(*infop)))
1718  		return -EFAULT;
1719  
1720  	unsafe_put_user(signo, &infop->si_signo, Efault);
1721  	unsafe_put_user(0, &infop->si_errno, Efault);
1722  	unsafe_put_user(info.cause, &infop->si_code, Efault);
1723  	unsafe_put_user(info.pid, &infop->si_pid, Efault);
1724  	unsafe_put_user(info.uid, &infop->si_uid, Efault);
1725  	unsafe_put_user(info.status, &infop->si_status, Efault);
1726  	user_write_access_end();
1727  	return err;
1728  Efault:
1729  	user_write_access_end();
1730  	return -EFAULT;
1731  }
1732  
1733  long kernel_wait4(pid_t upid, int __user *stat_addr, int options,
1734  		  struct rusage *ru)
1735  {
1736  	struct wait_opts wo;
1737  	struct pid *pid = NULL;
1738  	enum pid_type type;
1739  	long ret;
1740  
1741  	if (options & ~(WNOHANG|WUNTRACED|WCONTINUED|
1742  			__WNOTHREAD|__WCLONE|__WALL))
1743  		return -EINVAL;
1744  
1745  	/* -INT_MIN is not defined */
1746  	if (upid == INT_MIN)
1747  		return -ESRCH;
1748  
1749  	if (upid == -1)
1750  		type = PIDTYPE_MAX;
1751  	else if (upid < 0) {
1752  		type = PIDTYPE_PGID;
1753  		pid = find_get_pid(-upid);
1754  	} else if (upid == 0) {
1755  		type = PIDTYPE_PGID;
1756  		pid = get_task_pid(current, PIDTYPE_PGID);
1757  	} else /* upid > 0 */ {
1758  		type = PIDTYPE_PID;
1759  		pid = find_get_pid(upid);
1760  	}
1761  
1762  	wo.wo_type	= type;
1763  	wo.wo_pid	= pid;
1764  	wo.wo_flags	= options | WEXITED;
1765  	wo.wo_info	= NULL;
1766  	wo.wo_stat	= 0;
1767  	wo.wo_rusage	= ru;
1768  	ret = do_wait(&wo);
1769  	put_pid(pid);
1770  	if (ret > 0 && stat_addr && put_user(wo.wo_stat, stat_addr))
1771  		ret = -EFAULT;
1772  
1773  	return ret;
1774  }
1775  
1776  int kernel_wait(pid_t pid, int *stat)
1777  {
1778  	struct wait_opts wo = {
1779  		.wo_type	= PIDTYPE_PID,
1780  		.wo_pid		= find_get_pid(pid),
1781  		.wo_flags	= WEXITED,
1782  	};
1783  	int ret;
1784  
1785  	ret = do_wait(&wo);
1786  	if (ret > 0 && wo.wo_stat)
1787  		*stat = wo.wo_stat;
1788  	put_pid(wo.wo_pid);
1789  	return ret;
1790  }
1791  
1792  SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
1793  		int, options, struct rusage __user *, ru)
1794  {
1795  	struct rusage r;
1796  	long err = kernel_wait4(upid, stat_addr, options, ru ? &r : NULL);
1797  
1798  	if (err > 0) {
1799  		if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
1800  			return -EFAULT;
1801  	}
1802  	return err;
1803  }
1804  
1805  #ifdef __ARCH_WANT_SYS_WAITPID
1806  
1807  /*
1808   * sys_waitpid() remains for compatibility. waitpid() should be
1809   * implemented by calling sys_wait4() from libc.a.
1810   */
1811  SYSCALL_DEFINE3(waitpid, pid_t, pid, int __user *, stat_addr, int, options)
1812  {
1813  	return kernel_wait4(pid, stat_addr, options, NULL);
1814  }
1815  
1816  #endif
1817  
1818  #ifdef CONFIG_COMPAT
1819  COMPAT_SYSCALL_DEFINE4(wait4,
1820  	compat_pid_t, pid,
1821  	compat_uint_t __user *, stat_addr,
1822  	int, options,
1823  	struct compat_rusage __user *, ru)
1824  {
1825  	struct rusage r;
1826  	long err = kernel_wait4(pid, stat_addr, options, ru ? &r : NULL);
1827  	if (err > 0) {
1828  		if (ru && put_compat_rusage(&r, ru))
1829  			return -EFAULT;
1830  	}
1831  	return err;
1832  }
1833  
1834  COMPAT_SYSCALL_DEFINE5(waitid,
1835  		int, which, compat_pid_t, pid,
1836  		struct compat_siginfo __user *, infop, int, options,
1837  		struct compat_rusage __user *, uru)
1838  {
1839  	struct rusage ru;
1840  	struct waitid_info info = {.status = 0};
1841  	long err = kernel_waitid(which, pid, &info, options, uru ? &ru : NULL);
1842  	int signo = 0;
1843  	if (err > 0) {
1844  		signo = SIGCHLD;
1845  		err = 0;
1846  		if (uru) {
1847  			/* kernel_waitid() overwrites everything in ru */
1848  			if (COMPAT_USE_64BIT_TIME)
1849  				err = copy_to_user(uru, &ru, sizeof(ru));
1850  			else
1851  				err = put_compat_rusage(&ru, uru);
1852  			if (err)
1853  				return -EFAULT;
1854  		}
1855  	}
1856  
1857  	if (!infop)
1858  		return err;
1859  
1860  	if (!user_write_access_begin(infop, sizeof(*infop)))
1861  		return -EFAULT;
1862  
1863  	unsafe_put_user(signo, &infop->si_signo, Efault);
1864  	unsafe_put_user(0, &infop->si_errno, Efault);
1865  	unsafe_put_user(info.cause, &infop->si_code, Efault);
1866  	unsafe_put_user(info.pid, &infop->si_pid, Efault);
1867  	unsafe_put_user(info.uid, &infop->si_uid, Efault);
1868  	unsafe_put_user(info.status, &infop->si_status, Efault);
1869  	user_write_access_end();
1870  	return err;
1871  Efault:
1872  	user_write_access_end();
1873  	return -EFAULT;
1874  }
1875  #endif
1876  
1877  /**
1878   * thread_group_exited - check that a thread group has exited
1879   * @pid: tgid of thread group to be checked.
1880   *
1881   * Test if the thread group represented by tgid has exited (all
1882   * threads are zombies, dead or completely gone).
1883   *
1884   * Return: true if the thread group has exited. false otherwise.
1885   */
1886  bool thread_group_exited(struct pid *pid)
1887  {
1888  	struct task_struct *task;
1889  	bool exited;
1890  
1891  	rcu_read_lock();
1892  	task = pid_task(pid, PIDTYPE_PID);
1893  	exited = !task ||
1894  		(READ_ONCE(task->exit_state) && thread_group_empty(task));
1895  	rcu_read_unlock();
1896  
1897  	return exited;
1898  }
1899  EXPORT_SYMBOL(thread_group_exited);
1900  
1901  __weak void abort(void)
1902  {
1903  	BUG();
1904  
1905  	/* if that doesn't kill us, halt */
1906  	panic("Oops failed to kill thread");
1907  }
1908  EXPORT_SYMBOL(abort);
1909